exc_info inside an except clause will always return not None

When calling sys.exc_info from inside an except block, the returned variables will never be None, as defined by the standard library.

However, when trying to use one of the returned variables, mypy throws an error as the type is set as Optional[Type[BaseException]].

Here's the output:

> mypy test.py
test.py:8: error: Item "None" of "Optional[Type[BaseException]]" has no attribute "__name__"
Found 1 error in 1 file (checked 1 source file)

Here's the code I'm using to test:

import sys

# This causes the error
try:
    raise Exception
except Exception:
    ex, val, _ = sys.exc_info()
    print(f"Failed: {ex.__name__}: {val}")  # Line 8

# This does not
try:
    raise Exception
except Exception:
    ex, val, _ = sys.exc_info()
    if ex is not None:  # Pointless comparison
        print(f"Failed: {ex.__name__}: {val}")

I'm not sure if this is a bug or a missing feature?

Inizia con la riproduzione in test.py e confronta il tipo inferito da mypy per sys.exc_info() all’interno del blocco except con il comportamento della libreria standard descritto nell’issue. Conferma il risultato atteso eseguendo mypy sull’esempio: l’accesso a ex.name non dovrebbe richiedere il controllo superfluo di None.